I don't know why there are still people who hate him, even those who call him the writer's darling or his wife's savior. This hatred is completely unjustified, and any belittling of Leonardo shows a lack of understanding of the story. Most of the excuses given for hating him are superficial and have already been explained. I will explain it further here so the text may contain spoilers

In anime: You'll always find lame excuses for him not training, even though he's actually been training for more than one frame

\-Yuno also experienced a kind of psychological trauma. Imagine starting to adapt to a group that wasn't even recognized, and then suddenly Zenon comes along and kills them all. This contrasts with Asta, who wasn't affected by classism and racism, and who found himself compatible with the bulls.

\-Some also dislike Yuno in the anime because they find him annoying, but the problem is that he's in the character, and if you follow the series from the beginning, you'll find him not annoying at all. 

manga:Here you realize that most of his haters, who are manga followers, don't understand the story at all. 

One of the things that most bothers Asta's hostages is how he uses the Anti-Magic and Licht's swords. Firstly, Asta can give the Anti-Magic to those close to him, like the Black Bulls, and Yuno is no exception. As for its use, Licht's swords... As we know, Yuno possesses the spirit of Licht's son, and therefore Yuno has the right to use Licht's swords, even more so than Asta, since Asta is an anomaly and thus can use Licht's swords.

Another thing they hate is that he owns two books, one of which contains magic that belongs to the spirit of Ibn Licht, and the other contains star magic, which is his own magic since he is originally from the Spade tribe. When they fought against Zenon, they were killing each other inside the library, so it was only natural that Yuno would take his book and original magic.

Ultimately, anyone who hates him without justification is escalating the situation, and anyone who belittles him hasn't understood the whole story.

Yuno haters